In the 3GPP (3rd Generation Partnership Project), which is a standardization project of mobile communication systems, introduction of a user data transmission system using dual connectivity scheme has been examined. In this transmission system, connection is established between each of a plurality of base stations and user terminal, by which a plurality of data paths used for the transfer of user data are established.
In particular, examples of the data path established in dual connectivity include: a data path established between a core network and user equipment via one base station; and a data path established between a core network and user equipment, branching at one base station, one branched path thereof being established via another base station, and the other branched path thereof being established not via another base station. These data paths may be referred to as bearers.
A plurality of user plane architectures with different combinations of these data paths are proposed (see Non Patent Document 1).